1. Field of the Invention
This invention relates to a composition for use in the processing of semiconductor materials for use in the production of integrated circuits, more particularly to a semiconductor cleaning solution and to methods for its production and use.
2. Brief Description of the Prior Art
Integrated circuit elements are produced by coating a semiconductor substrate surface, e.g. a silicon wafer, possibly after a layer of conductive metal has been applied to the surface, with a layer of photoresist material, applying to the photoresist surface a pattern corresponding in either the positive or negative sense to the desired circuit element, activating the printed photoresist layer by exposure to suitable activating radiation, such as light or x-rays, to make the printed and unprinted areas of it differentially soluble in a developing solution and treating the activated photoresist layer with the developing solution to remove the soluble areas of the photoresist layer either to expose the substrate surface for the application thereto of the desired circuit element, which may be by deposition of a conductive metal or metal oxide or by ion implantation with, for example, boron ions into the body of the substrate, or to expose a pre-applied conductive layer which may be etched to remove all but the desired circuit element and finally stripping from the semiconductor surface the residue of the photoresist layer. This procedure may be repeated to build up a circuit comprising superimposed circuit elements.
The number of independent electronic circuit elements included in a single integrated circuit design has increased greatly as technology capabilities have progressed from small scale integration through to very large scale integration which may correspond to about 10.sup.5 transistor elements per semiconductor chip or wafer element. The accompanying decrease in line widths, line spacing and line thickness has led to a great increase in the sensitivity of the finished product to the presence of contaminants on the wafer surface making it increasingly difficult to maintain a reasonable level of yield of finished integrated circuits.
Contaminants may result from a number of sources. They may be, for example, thin, possibly almost monomolecular, films of an organic nature resulting from previous photoresist layer traces or from organic matter emanating from operatives which may be deposited by handling or even from the air. Contaminants may also be particulate in nature and may for example be of an inorganic nature deposited from etchant components.
Because of the necessity to remove, so far as possible, all contaminant traces from a semiconductor surface before the application of a circuit element, a further circuit element or before use, there has developed a specialised range of semiconductor cleaning solutions. While these cleaning solutions may bear superficial resemblances to photoresist stripping solutions they operate on a different principle in that, in the case of stripping solutions using sulphuric acid and hydrogen peroxide, the active species, permonosulphuric acid, is relatively ineffective for cleaning purposes.
Japanese patent publication No. 61-105847 describes a process for cleaning semiconductor surfaces comprising producing hot sulphuric acid having a typical concentration of from 97.4% to 98% by weight by the addition of water to oleum, the heating of the acid being a result of the reaction between the water and the sulphur trioxide in the oleum, to generate sulphuric acid, mixing the hot concentrated acid with aqueous hydrogen peroxide at a position adjacent to the surface to be cleaned, thereby generating further heat as a result of the dilution of the concentrated acid, to give a treating mixture having a temperature, essentially, of at least 100.degree. C., and contacting the surface with that treating mixture. Under such circumstances there is almost instantaneous decomposition of the hydrogen peroxide to produce nascent oxygen as an active cleaning species.
U.S. Pat. No. 3728154 describes a process for cleaning semiconductor surfaces using freshly prepared diluted sulphuric acid having a temperature deriving from the heat of dilution of 150.degree. C. the use being completed by the time the temperature has decayed to 130.degree. C. The freshly prepared diluted acid is postulated in the patent to have special properties and if it is allowed to cool to room temperature it is highly ineffective and if it is then reheated to 150.degree. C. it is much less effective than the original fresh solution.
Long term storage semiconductor cleaning solutions based on sulphuric acid and hydrogen peroxide are not known and it is an object of the present invention to provide such and a method for their production.